Thio and dithiocinnamic acids as antifoggants and stabilizers



United States Patent 3,507,658 THIO AND DITHIOCINNAMIC ACIDS AS ANTI- FOGGANTS AND STABILIZERS Fritz Dersch, Binghamton, and Sally L. Paniccia, Endwell, N.Y., assignors to GAF Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 8, 1967, Ser. No. 621,427 Int. Cl. G03c 5/30, 1/34 U.S. Cl. 96109 11 Claims ABSTRACT OF THE DISCLOSURE Thio and dithiocinnamic acid antifoggant and stabilizer compounds for use in photographic elements and/ or one or more of the processing solutions associated with postexposure treatment.

This invention relates in general to photography and in particular to the provision of novel antifogging and stabilizing compounds for use in connection with the preparation and/or processing of photographic silver halide emulsions.

It is Well known that light-sensitive materials such as gelatin-silver halide emulsions exhibit a marked tendency to fog. The term fog as used in the photographic art connotes that portion of the density obtained upon development which arises by virtue of factors other than the photographic exposure. The fog may be attributable to a number of influences including for example, excessive ripening of the emulsion, prolonged storage of the film and especially under conditions of elevated temperature and/or humidity, as well as by prolonged development of the exposed emulsion and the like. In general, the fog may be of two types, namely, yellow fog and chemical (gray) fog. The yellow fog, sometimes referred to as colored or dichroic fog, is essentially a colloidal deposit of silver, the color intensity and general appearance of which are determined by the minute particle size and degree of subdivision. The fog is chiefly yellow in color and is most apparent in the lighter portions of the negative. The color may vary, however, and the colloidal silver particles may, for example, appear green by reflected light and yellow or red by transmitted light.

On the other hand, the so-called chemical fog, or gray fog, is the more common and is formed in a number of ways. As mentioned hereinbefore, such fog may be caused by the nucleation of silver on or in the silver halide grains due to inadvertent exposure, excessive ripening of the emulsion, storage of the film under severe conditions of temperature and/ or humidity, etc. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulphur compounds, hydrogen peroxide vapors and strongly reducing materials such as those present in the developer solution. In any event, and irrespective of the cause, the fog will usually manifest itself as a spurious density extant over the entire area of the sensitive coating and typically, is substantially nonuniform.

To overcome or otherwise alleviate the aforedescribed disadvantages it has become a recognized practicec in the photographic art to add certain chemical stabilizer compounds to the light-sensitive emulsion at some stage of its preparation which purportedly function to enhance their photographic stability to an appreciable extent. However, in the vast majority of instances, the stabilizing and antifogging compounds heretofore employed for such purposes have provided only marginal improvement since they are often characterized by the disadvantage that upon addition to the emulsion they cause a loss of speed and/or contrast of the emulsion or otherwise deleteri- 3,507,658 Patented Apr. 21, 1970 ously affect its sensitometric characteristics. The loss in speed is particularly pronounced in those regions of the spectrum to which the emulsions are optically or dye sensitized.

In accordance with the discovery forming the basis of the present invention, it has been found that the antifogging and stabilization characteristics of light-sensitive silver halide emulsions can be synergistically modified to advantage by the utilization of a particular class of chemical compounds in connection with the preparation and/or processing of such emulsions.

Thus, a primary object of the present invention resides in the provision of improved antifogging and stabilizer compounds in which the foregoing and related disadvantages are eliminated or at least mitigated to a substantial degree.

Another object of the present invention resides in the provision of light-sensitive silver halide emulsions containing a compound which stabilizes the emulsion against fogging while exhibiting little, if any, tendency to reduce the speed or contrast of such emulsions.

A further object of the present invention resides in the provision of light-sensitive silver halide emulsions and photographic elements prepared therewith containing an antifogging compound which is substantially devoid of any tendency to reduce the sensitivity of the emulsion to light of longer wave length due to the presence of one or more sensitizing dyes.

A still further object of the present invention resides in the provision of a process for the treatment of an exposed photographic silver halide emulsion wherein at least one of the stepsof pretreating or developing the emulsion is effected in the presence of a novel stabilizing compound to be more fully described hereinafter.

The attainment of the foregoing and related objects is made in accordance with the broader aspects of the present invention by the incorporation in a light-sensitive photographic element, e.g., silver halide emulsion, developing solution and/or pretreatment solution of an antifoggant and stabilizer compound comprising certain thio and dithiocinnamic acids characterized by the following general formula:

I. wherein X represents a member of the group consisting of a hydrogen atom and a sulfur atom and n represents a whole positive integrer having a value of from 1 through 2, inclusive with the proviso that when X is a hydrogen atom the value of n is equal to l and X is a sulfur atom the value of n is equal to 2.

While the above general formula is indicative of the class of thiocinnamic and dithiocinnamic acids which are operable to produce the desired antifogging effects, it is generally believed that such effects are attributable to the presence of the thiocinnamyl structure and not necessarily, dependent upon the particular isomeric relationship of the thio radical and the acrylic radical; although the isometric relationship cannot be entirely discounted.

Representative thiocinnamic and dithiocinnamic acids of the class described above, which find immediate and practical utility in accomplishing the objects of the present invention, include for example the following:

o-meraptocinnamic acid m-mercaptocinnamic acid pmercaptocinnamic acid o,o-dithiocinnamic acid p,p-dithiocinnamic acid m,m-dithiocinnamic acid According to those embodiments of the present invention wherein the thiocinnamic compound is added to the light-sensitive silver halide emulsion per se, the antifoggant may conveniently be incorporated into the silver halide emulsion as a ripening final or as a coating final. Ripening finals are added during the ripening or the sensitivity increasing stage of the emulsion making process, whereas coatin finals are added to the silver halide emulsion just prior to the coating of the emulsion on a suitable support, such as, for example, paper, glass or film.

The addition of the antifoggants can be made before, during, or after the addition of the soluble silver salt to the soluble halide in the presence of a suitable carrier or colloid, such as gelatin, polyvinyl alcohol, solubilized casein, albumin and the like.

' The amount of antifogging agent employed as additives to the light-sensitive emulsions varies from about 0.1 to about 50 milligrams of antifoggant per 0.6 mole of silver halide. When the antifogging agents are employed as ripening finals it has been found advantageous to employ them in amounts in the range of from about 0.1 to about 25 milligrams per 0.6 mole of silver halide, whereas when the antifogging agents are employed in coating finals, it has been found advantageous to employ amounts in the range of from about 0.5 to about 50 milligrams of antifoggant per 0.6 mole of silver halide. Obviously, the development of optimum characteristics within the ranges set forth above will depend, in part, upon the type of emulsion employed and can be readily determined in each case.

The stabilizer compounds contemplated herein can be applied in a variety of ways to impart stability to photographic elements. As previously mentioned, they may be included as a constituent of the emulsion layer, of a surface layer over the emulsion or alternatively, over the base or support.

Further embodiments of the present invention contemplate the addition of such compounds to at least one of the developing, fixing, washing, drying, etc., solutions utilized in the processing of the exposed emulsion. For example, when utilized in the washing step the stabilizer can be applied to the otherwise finished photographic element by immersing same in an alcohol, e.g., methanol or alcohol-water solution in the case of the free acid derivatives while the salt derivatives may be employed efiectively as simple water solutions.

In general, it is found that the improvements provided by the present invention are particularly manifest according to procedures whereby development is effected in the presence of said stabilizer compounds. This, of course, would be the case should the stabilizer be included in the light-sensitive photographic element, the developing solution and/or suitable developer prebath. In any event, when incorporated into the photographic developer or other processing bath, the stabilizers of the present invention are preferably employed in concentrations ranging from about 1 to about 50 milligrams per liter of solution, with a range of about milligrams to about 20 milligrams per liter being particularly preferred.

In addition to being useful in orthochromatic and panchromatic emulsions, the stabilizers may also be used in non-sensitized emulsions, X-ray emulsions, paper emulsions, color emulsions and the like. If used with sensitizing dyes, they may be added to the emulsion before or after dye addition. Moreover, the present stabilizers may also be employed in conjunction with other known antifoggants and stabilizers, reduction stabilizers, metal and noble metal sensitizers or in combination with other additive agents and the like.

The stabilizer may also be employed in gelatin or other water-permeable colloids including polyamides or a mixture of gelatin with a polyamide as described in U.S. Patent 2,289,776; polyvinyl alcohol and gelling compound as described in U.S. Patent 2,249,537; polyvinyl acetaldehyde acetal resins and partially hydrolyzed acetate resins 4 described in U.S. Patents 1,939,422 and 2,036,092; cellulose derivatives, e.g., cellulose nitrate, cellulose acetate, and the lower fatty acid esters of cellulose including sample and mixed esters and ethers of cellulose and the like.

When preparing the photographic emulsion in accordance with the present invention, a solution of the stabilizer in a suitable solvent, such as water, alcohol, dimethyl formamide or alcohol-water mixture adjusted to a neutral or slightly alkaline pH, i.e., about 7.5 to 10, is made up and the solution mixed with the emulsion at any convenient stage during its preparation, but preferably during ripening or just prior to coating.

The preparation of the mercaptocinnamic acids is described in Organic Chemistry 27, 283541 (1962). The disulfides corresponding thereto are readily prepared by oxidation of the corresponding mercaptocinnamic acid precursor in accordance with well known oxidation procedures.

The following examples will serve to illustrate the practice of the invention.

EXAMPLE I A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added such as sensitizing dyes and hardening agents. A 0.1% solution of mercaptocinnamic acid was added to the emulsion as an antifoggant and stabilizer. The emulsion samples contained about 0.6 mole of silver halide. The so-prepared emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type 1B Sensitometer and developed in a developer of the following composition:

Grams Metol 1.5 Sodium sulfite, anhydrous 45 Sodium bisulfite 1 Hydroquinone 3 Sodium carbonate, monohydrated 6 Potassium bromide 0.8 Water to make 1 liter.

' Relative Oven Oven Quantity of Speed at Fog at; Fog at Speed at Compound Used 3 Dev. 12 Dev. 3' Dev. 3 Dev.-

0 100 .52 .23 95 10 mg. per kilo 100 .37 .17 95 EXAMPLE II Relative Oven Oven Quantity of Speed at Fog at Fog at; Speed at Compound Used 3' Dev 12 Dev. 3 Dev. 3' Dev.-

0. 100 0. 42 0. 27 90 2.5 mg. per liter 100 0. 32 0. 27 9O 5 mg. per liter 100 0.30 0.25 90 10 mg. per liter 100 0. 27 0. 24 90 What is claimed is: 1. A light-sensitive silver halide emulsion containing as an antifoggant and stabilizer, a stabilizing amount of a compound of the following structural formula:

CH=CHCOOH wherein X represents a member of the group consisting of a hydrogen atom and a sulfur atom and n represents a Whole positive integer having a value of from 1 through 2, inclusive with the proviso that when X is a hydrogen atom the value of n is equal to 1 and when X is a sulfur atom the value of n is equal to 2.

2. A light-sensitive silver halide emulsion according to claim 1, wherein said stabilizer comprises o-mercaptocinnamic acid.

3. A light-sensitive silver halide emulsion according to claim 1, wherein said stabilizer comprises m-mercaptocinnamic acid.

4. A light-sensitive silver halide emulsion according to claim 1, wherein said stabilizer comprises p-mercaptocinnamic acid.

5. A light-sensitive silver halide emulsion according to claim 1, wherein said stabilizer comprises o,o'-ditl1iocinnamic acid.

6. A light-sensitive silver halide emulsion according to claim 1, wherein said stabilizer comprises p,p'-dithiocinnamic acid.

7. A light-sensitive silver halide emulsion according to claim 1, wherein said stabilizer comprises m,m'-dithiocinnamic acid.

8. A light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion, said light-sensitive material containing as an antifoggant and stabilizer, a stabilizing amount of a compound of the following structural formula:

(IfH=CHCOOH wherein X represents a member of the group consisting of a hydrogen atom and a sulfur atom and n represents a whole positive integer having a value of from 1 through 2, inclusive with the proviso that when X is a hydrogen atom the value of n is equal to 1 and when X is a sulfur atom the value of n is equal to 2.

9. A light-sensitive photographic material according to claim 8 wherein said antifoggant and stabilizer compound is present in said light-sensitive silver halide emulsion layer.

10. A light-sensitive photographic material according to claim 8 wherein said antifoggant and stabilizer compound is present in a layer in contact with said lightsensitive silver halide emulsion layer.

11. A process of treating an exposed silver halide emulsion which comprises developing said emulsion in the presence of a stabilizing amount of a compound of the following structural formula:

wherein X represents a member of the group consisting of a hydrogen atom and a sulfur atom and n represents a whole positive integer having a value of from 1 through 2, inclusive with the proviso that when X is a hydrogen atom the value of n is equal to 1 and when X is a sulfur atom the value of n is equal to 2.

References Cited UNITED STATES PATENTS 3,226,232 12/1965 Dersch et al. 96-109 X 3,244,522 4/1966 Clementi et al. 96109 X NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner US. Cl. X.R. 9666.5 

